It is well known to employ foaming or emulsifier compositions based on surface-active agents for extinguishing fires of liquid solvents. These emulsifiers, known as fire-extinguishing emulsifiers, are generally thrown forward onto the fire in the form of a foam obtained by mixing them under pressure with water.
A particular class of fire-extinguishing emulsifiers is known under the designation of AFFF, for "Aqueous Film-Forming Foam" or "Agent Forming a Floating Film". AFFF compositions enable fires caused by liquid hydrocarbons to be rapidly extinguished. AFFF emulsifiers contain fluorine-containing surface-active agents which have a very low value of surface tension. As a result, these surfactants make it possible to produce a foam which, on separation, forms an aqueous film floating above the surface of the hydrocarbon. This aqueous film makes it possible to extinguish the fire and to prevent a possible reignition of the hydrocarbon.
However, emulsifiers of AFFF type, while being effective for extinguishing fires due to hydrocarbon liquids, are not effective in the case of fires caused by polar solvents, especially alcohols, ketones and esters of low molecular weights. In fact, with polar solvents of this type the foams obtained from AFFF emulsifiers are rapidly dissolved and destroyed.
A particular class of emulsifiers has been developed for fighting fires produced by such a polar solvent. These emulsifiers include fluorine-containing surfactants and a water-soluble polymer which precipitates in contact with the polar solvent, with the result that it forms a protective layer between said polar solvent and the foam. These emulsifiers are known under the designation A4P, for "Agent Producing a Multipurpose Protective Film" or under the designation ARAFFF, for "Alcohol Resistant Aqueous Film-Forming Foam". It is the designation ARAFFF that is employed in the present specification.
Emulsifiers of ARAFFF type are effective both on fires caused by hydrocarbon solvents and polar solvents.
In addition to the fluorine-containing surfactants, that is to say surfactants which have a perfluoroalkyl residue, emulsifiers of AFFF and ARAFFF type include surfactants not containing fluorine.
Thus, international applications WO 91/01160 and WO 92/15371 describe fire-extinguishing emulsifiers of AFFF and ARAFFF type containing nonionic surfactants of the alkylpolyglycoside type. The foremost advantage of these surfactants of alkylpolyglycoside type is that they allow a decrease in the concentration of the fluorine-containing surfactants in the emulsifiers of AFFF type. They also make it possible to reduce the content of water-soluble polymer in emulsifiers of ARAFFF type.
However, the Applicant Company has been able to ascertain that surfactants of alkylpolyglycoside type have the disadvantage of having to be used in combination with another, third, surfactant not containing fluorine with a view to obtaining a short emulsifier expansion time. The expansion time is the time needed for the emulsifier mixed with water to form the foam used for extinguishing fires.
It has also been ascertained that the foams formed from fire-extinguishing emulsifiers of AFFF and ARAFFF type including alkylpolyglycosides, even when the latter are used in combination with other surfactants, are relatively rapidly destroyed once the fire is extinguished. Risks of fire restarting are then possible.